The proposed research is designed to study the genetic basis of dominance and mating preference in wild house mice. About 30% of wild house mice are heterozygous for a variable recessive allele (+/t) at the T locus. Although t-alleles are recessive lethals, they persist in high frequency in mouse populations because they are associated with meiotic drive. Previous research, testing mice in arenas, has shown that possession of a t-allele is highly correlated with dominance in wild house mice. However, there is some evidence that female mice may attempt to avoid mating with males carrying these alleles. The purpose of the proposed research is to examine the interaction between genotype of wild mice at the T locus and their dominance status and mating behavior in a semi-natural environment. I plan to record their dominance status, associational preferences as measured by indices of approach and avoidance, and reproductive success. Paternity of young will be assessed by electrophoretic analysis. This research should further our understanding of the genetic and evolutionary mechanisms producing aggressive behavior, a topic which is receiving so much attention in medicine, psychiatry and psychological thinking in general.